Techniques for setting up traffic channels in a communications system

ABSTRACT

A control channel supporting traffic control in epochs is divided into two control subchannels each being less than or equal to about a half epoch in duration and occurring serially in time. Slot allocation data may be transmitted and received independently over the subchannels. One subchannel may be used for transmitting forward slot allocation data and the other subchannel may be used for transmitting reverse slot allocation data. The channel split into two subchannels may be a paging channel. The forward and reverse slot allocation data may be transmitted between a base station processor and field unit. Forward and reverse traffic data may be staggered by at least about half an epoch. Transmission of traffic data happens within about two epochs after the assignments.

RELATED APPLICATION(S)

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/350,835, filed Jan. 22, 2002, the entire teachings ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] In a wireless telecommunications system, radio channels provide aphysical link between communications units. The equipment in such asystem typically includes a base station processor in communication witha network such as the Public Switched Telephone Network (PSTN), in thecase of voice communications, or a data network, in the case of datacommunications, and one or more access terminals in communication with aplurality of end user computing devices, such as user PCs. Thecombination of an access terminal and computing device(s) may bereferred to as a field unit. The wireless channels include forwardchannels, for message transmission from the base station processor tothe subscriber access units, and reverse channels, for messagetransmission to the base station processor from the field units.

[0003] In the case of a wireless data system such as may be used toprovide wireless Internet access, each base station processor typicallyserves many access terminals, which in turn serve many end usercomputing devices. The wireless channels, however, are a limitedresource, and are therefore allocated by a scheduler among the fieldunits served by the base station processor. The scheduler allocates thewireless channels among the field units on a traffic demand basis.

[0004] One way of supporting on-demand access among multiple users isreferred to as Time Division Multiple Access (TDMA), where each of thewireless channels are allocated to specific connections only for certainpredetermined time intervals or time slots. A second way of supportingon-demand access among multiple users is referred to as Code DivisionMultiple Access (CDMA), which allows multiple users to share the sameradio spectrum. Instead of dividing a Radio Frequency (RF) spectrum intonarrow channels (e.g. 30 kHz each in analog wireless systems), CDMAspreads many channels over a broad spectrum (1.25 MHZ in the case of theNorth American CDMA standard known as IS-95). To separate a particularchannel from the other channel using the same spectrum at the same time,a unique digital code called a pseudo-random (i.e., pseudo-noise or PN)code is assigned to each user. Many users (up to 64 for IS-95) share thesame spectrum, each using their unique code, and decoders separate thecodes at each end in a process similar to a tuner that separatesdifferent frequencies in more conventional systems.

[0005] The PN codes used for communication channel definitions typicallyhave a defined code repeat period or code epoch. For each such epochduration (also called a slot), a base station central controlling systemor processor can further schedule assignments of forward trafficchannels (forward slot allocations or “FSAs”) and reverse trafficchannels (reverse slot allocations or “RSAs”) to active mobile units foreach epoch. This is typically done in such a way that all channels areassigned to active users as much as possible. It typically takes apredetermined amount of time for the allocation command to be receivedand to configure the demodulators before receiving the new code channel.In particular, when a PN code is reassigned to a different userconnection, it typically takes a determined period of time for the codedemodulators in the receiver to lock in the new code. This in turnintroduces latency in the reception of the data packets that must travelon the coded channel.

[0006] To coordinate traffic channels, the base station processorcommunicates with a given field unit in the following manner. First, thebase station processor checks to make sure there is an availablechannel. Second, the base station processor sends a message to the givenfield unit to set up the available channel. The given field unitprocesses the message (2-3 epochs) to set-up the channel and sends anacknowledgment (1-2 epochs) confirming set-up complete. To tear down thechannel, the base station processor sends a message to the given fieldunit, which processes the command (1-2 epochs) and sends back anacknowledgment (1-2 epochs).

SUMMARY OF THE INVENTION

[0007] A communications system employing the principles of the presentinvention reduces packet latency, which, in turn, improves response timefor setting up traffic channels in a communications system, such as anon-demand access, packet switched, CDMA communications system. Theseimprovements apply to both forward and reverse traffic channels.

[0008] Channel code assignments are pipelined from a base transceiverstation (BTS) down to all of the mobile units in a cell zone associatedwith the BTS so the actual transmission of traffic data can begin,within about two epochs after the channel assignments. Keeping thisdelay to a minimum is what improves the latency.

[0009] There are at least three features that help in keeping this delayshort: (i) dividing a control channel, such as the paging channel, intocontrol subchannels, such as two control subchannels or half-channels(optionally referred to as a forward half-channel and reversehalf-channel), where, in the case of two control subchannels, the newsplit paging channels may be less than or equal to about half theduration of the standard control channels (e.g., half an epoch), (ii)staggering the forward and reverse traffic channels by about half anepoch, and eliminating the acknowledgment returned to the BTS, since theslot allocation/deallocation commands are redundant (i.e., sent multipletimes for a contiguous slot allocation). Forward and reverse slotallocation data may be transmitted in objects less than or equal toabout a half epoch duration and transmitted from the base stationprocessor to the field units in respective forward and reversesubchannels, e.g., paging subchannels.

[0010] These two features can improve latency by one or two epochs perforward and reverse channel allocation. This, in turn, shows up as anoticeable improvement in response time to the user.

[0011] In one embodiment, the present invention may be used in linklayer software on the base station and field units to improve channellatency and can be used by any system using a CDMA packet switchedcommunications system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

[0013]FIG. 1 is a block diagram of a wireless communications systemsuitable for performing wireless paging channel techniques describedherein;

[0014]FIG. 2 is a timing diagram of a technique for allocating a forwardchannel according to the principles of the present invention used in thesystem of FIG. 1;

[0015]FIG. 3 is a timing diagram of a technique for allocating a reversechannel according to the principles of the present invention used in thesystem of FIG. 1; and

[0016]FIG. 4 is a timing diagram of an alternative technique forallocating the reverse channel according to the principles of thepresent invention used in the system of FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0017] A description of preferred embodiments of the invention follows.

[0018]FIG. 1 shows a wireless telecommunications system suitable forreducing packet latency according to the principles of the presentinvention. A plurality of data processing devices, such a personalcomputers (PCs), Personal Digital Assistants (PDAs), data enabled mobilephones or the like (collectively the PCs) 12 a-12 e are in communicationwith a subset of access terminals (ATs) 14 a-d via a wired connection20. The wired connection 20 typically conforms to a wired protocol suchas Ethernet with embedded TCP/IP or UDP/IP packets. The combination of aPC 12 and AT 14 may be referred to as a field unit 15 or remote unit. Inthe case of the second field unit 15 b, the PC associated with the AT 14b is built into the AT 14 b and is therefore not shown.

[0019] The field units 15 a-15 d are in wireless communication with abase station processor (BSP) 16 via a wireless link 26. The wirelesslink 26 conforms to a wireless protocol such as IS-95 or anotherwireless protocol which supports communications via an RF medium.

[0020] The base station processor 16 is also connected to a publicaccess network 18, such as the Internet, via an internetworking gateway24. The internetworking gateway 24 is typically a bridge, router, orother connection to a network backbone and may be provided by a remoteprovider, such as an Internet Service Provider (ISP). In this manner, anend user at the PC 12 is provided a wireless connection to a publicaccess network 18 via the AT 14 and the base station processor 16.

[0021] Typically, a user PC 12 sends a message over a wired link 20,such as a local area network or bus connection, to the field unit 15.The field unit 15 sends a message via the wireless link 26 to the basestation processor 16. The base station processor 16 sends the message tothe public access network 28 via the internetworking gateway 18 fordelivery to a remote node 30 located on the network 28. Similarly, theremote node 30 located on the network can send a message to the fieldunit 15 by sending it to the base station processor 16 via theinternetworking gateway 24. The base station processor 16 sends themessage to the access terminal 14 serving the PC 12 via the wirelesslink 26. The access terminal 14 sends the message to the PC 12 via thewired link 20. The PC 12 and the base station processor 16 can thereforebe viewed as endpoints of the wireless link 26.

[0022] As indicated above, there are typically many more field units 15than there are available wireless channel resources. For this reason,the wireless channels are allocated according to some type ofdemand-based multiple access technique to make maximum use of theavailable radio channels. Multiple access is often provided in thephysical layer or by techniques that manipulate the radio frequencysignal, such as Time Division Multiple Access (TDMA) or Code DivisionMultiple Access (CDMA) techniques. In any event, the nature of the radiospectrum is such that it is a medium that is expected to be shared. Thisis quite dissimilar from the traditional wired environment for datatransmission in which a wired medium, such as a telephone line ornetwork cabling, is relatively inexpensive to obtain and to keep openall the time.

[0023] In a typical wireless transmission, a send message often resultsin a return acknowledgment message. A wireless channel is allocated tosend the message, and a second wireless channel is allocated in theopposite direction to send the return message. Wireless channelallocation can occur by a variety of methods well known in the art.

[0024]FIG. 2 is a timing diagram 30 indicating latency improvements(i.e., reductions) for allocating the forward channels of the wirelesssystem 10. This improvement is described for a packet switched CDMAcommunications system but may be used to reduce latency in TDMA or othermultiplexing systems that have forward slot allocations. In the presentCDMA case, the forward link—from base station processor 16 to fieldunits 15—includes a paging channel, multiple traffic channels, andmaintenance channels. The timing diagram 30 includes relative timing ofsignals in the paging and traffic channels.

[0025] The timing diagram 30 is separated horizontally into four epochs32-1 through 32-4 and vertically into a sequence of steps used totransmit and activate the forward channels. A first step 34 is providedin which the base station processor 16 loads forward slot allocationsinto a paging/F buffer object. The paging/F buffer object includestypical overhead information as a standard buffer object of the priorart, but only includes traffic channel allocation data for the forwardtraffic channels and, thus, is only a half epoch in duration. A secondstep 36 is provided in which the paging/F buffer object is transmittedby the base station processor 16 to the field unit 15 and demodulated bythe field unit 15. In a third step 38, the field unit 15 decodes thepaging/F buffer object, extracts forward channel assignments, andconfigures its receiver(s) for the forward channels. In a fourth step40, a half epoch after decoding the paging/F buffer object, the fieldunit 15 decodes data traffic on the forward channels.

[0026] The paging channel may be split into two subchannels, such as onefor transmitting forward slot allocation data and one for transmittingreverse slot allocation data. Each subchannel may be less than or equalto about half an epoch long and may be referred to as a “forward”half-channel and a “reverse” half-channel.

[0027] It should be understood that the paging channel may be furthersubdivided into smaller slotted subchannels of less than or equal toabout 1/n^(th) of an epoch long, where n is the number of subchannels.Further, the lengths of the subchannels may be different, so long as thecombined length is less than or equal to an epoch. It should also beunderstood that the subdivided channel may be a channel other than thepaging channel, such as a maintenance channel or an unused trafficchannel.

[0028] The rest of the discussion assumes the paging channel is splitinto two subchannels, referred to as half-channels.

[0029] As shown in FIG. 2, step 36, the forward paging/F object loadedin the first epoch 32-1 is transmitted over the first half-channel inthe first half epoch of epoch 32-2 and also demodulated in the samefirst half of the epoch 32-2. The second half of the epoch 32-2 is usedby the field unit 15 to decode the slot allocation data, sent in theform of messages or control data, and to configure the forward trafficchannels. This means the forward channel assignments can be placed intothe forward half-channel one epoch (e.g., epoch 32-2) and the forwardtraffic can then be placed into the very next epoch (e.g., epoch 32-3).This saves a whole extra epoch in time that would normally be needed todemodulate a standard, full paging channel, buffer object, which would,for example, fill the entire epoch 32-2 and not be ready for forwardtraffic data until two epochs later, epoch 32-4.

[0030]FIG. 3 is a timing diagram 50 indicating latency improvements(i.e., reductions) for allocating the reverse channels of the wirelesssystem 10. The forward epochs 32 and a corresponding set of reverseepochs 52 are provided to show timing relationships between the forwardand reverse directions. The process defined in FIG. 3 includes reversepaging/R steps 54 a-60 that parallel the forward paging/F steps 34-40provided in FIG. 2.

[0031] Referring to FIG. 3, as discussed above, the paging channel issplit into two half-channels. The first half-channel may be used fortransmitting the ½ size paging/F object (as discussed above), and thesecond half-channel may be used for transmitting a ½ size paging/Robject. For reverse traffic, the ½ size paging/R objects containsoverhead data of standard objects, as in the case of the ½ size paging/Fobjects, and, similarly, the ½ size paging/R objects also include theReverse Slot Allocation (RSA) data that can be sent and demodulated inthe second half-epoch of the second epoch 32-2. Compare step 36 withstep 56 to see the timing relationship of the forward and reversehalf-channels.

[0032] The reverse epoch 52 may be staggered by half an epoch to closeup the amount of delay between sending Reverse Slot Allocations (step56) and actually transmitting reverse traffic (step 60). This means thereverse channel assignment can be transmitted in the reversehalf-channel in one epoch 52-2 and, in the following epoch 52-3, reversetraffic data can be sent up the reverse channel defined by the reverseslot allocation data.

[0033] Splitting the paging channel into two channels of half-epochduration and independently transmitting the paging/F and paging/Robjects saves an extra epoch in time that would normally be needed todemodulate a full, standard, paging channel having the paging/F andpaging/R objects concatenated and transmitted together in a full epoch.Also, by making the paging/R object only ½ epoch, the base stationprocessor 16 can delay loading the Reverse Slot Allocations by half anepoch (e.g., start the loading at the start of the first reverse epoch52-1 rather than at the start of the first forward epoch 32-1), whichallows late requests get into the allocations that normally would needto wait another epoch.

[0034] This system can be improved even further if the base stationprocessor 16 delays the loading of the Reverse Slot Allocations 54 auntil after the first forward epoch 32-1, as defined by a loading step54 b in the timing diagram 50 of FIG. 4.

[0035] It is assumed that the Slot allocations arrive at the physicallayer and are sent between the base station processor 16 and field unit15 in one epoch. This results in another one-half epoch improvement onlatency overall.

[0036] It should be understood that the process described herein may beprovided by software, firmware, or hardware. The software may be storedin RAM, ROM, optical or magnetic disk, or other storage media. Thesoftware is loaded and executable by a processor that interacts withdevices capable of providing wire or wireless communication functionsdescribed herein or known to operate in the system 10 of FIG. 1. Thesoftware may be distributed by physical or wireless distribution methodscommonly used in commerce.

[0037] While this invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A method for traffic channel set-up in a timedivision multiplexed (TDM) communications system having TDM slotsapproximately equivalent to a time interval of a pseudo-noise (PN) codeepoch, comprising: dividing a control channel into a first controlsubchannel of less than or equal to about a half epoch in duration and asecond control subchannel of less than or equal to about a half epoch induration in the same control channel, the first and second controlsubchannels occurring serially in time; and independently transmittingslot allocation data in the first and second control subchannels toallocate respective TDM slots.
 2. A method according to claim 1 whereinthe control channel is a paging channel.
 3. A method according to claim1 wherein the step of transmitting slot allocation data includestransmitting forward slot allocation data in the first controlsubchannel and transmitting reverse slot allocation data in the secondcontrol subchannel.
 4. A method according to claim 3 wherein the step oftransmitting the slot allocation data includes separating the forwardand reverse slot allocation data into amounts allowing for processing ofthe data within about the next epoch, respectively, after reception. 5.A method according to claim 3 further including staggering transmissionof a reverse traffic channel defined by the reverse slot allocation datafrom transmission of a forward traffic channel defined by the forwardslot allocation data.
 6. The method according to claim 5 wherein thestep of staggering is at least about one-half epoch.
 7. The methodaccording to claim 3 further including collecting reverse channelallocation requests during transmission of slot allocation data over thefirst subchannel.
 8. An apparatus for traffic channel set-up in a timedivision multiplexed (TDM) communications system having TDM slotsapproximately equivalent to a time interval of a pseudo-noise (PN) codeepoch, the apparatus, comprising: a processor to divide a controlchannel into a first control subchannel of less than or equal to about ahalf epoch in duration and a control second subchannel of less than orequal to about a half epoch in duration in the same control channel, thefirst and second control subchannels occurring serially in time; and atransmitter coupled to the processor to transmit independently slotallocation data in the first and second control subchannels to allocaterespective TDM slots.
 9. The apparatus according to claim 8 wherein thecontrol channel is a paging channel.
 10. The apparatus according toclaim 8 wherein the transmitter transmits forward slot allocation datain the first control subchannel and reverse slot allocation data in thesecond control subchannel.
 11. The apparatus according to claim 10wherein the processor separates the forward and reverse slot allocationdata into amounts allowing for processing of the data within about thenext epoch, respectively, after reception.
 12. The apparatus accordingto claim 10 wherein the transmitter staggers transmission of a reversetraffic channel defined by the reverse slot allocation data from thetransmission of a forward traffic channel defined by the forward slotallocation data.
 13. The apparatus according to claim 12 wherein thestaggering is at least about one-half epoch.
 14. The apparatus accordingto claim 10 wherein the processor collects reverse channel allocationrequests during the transmission of slot allocation data over the firstcontrol subchannel.
 15. An apparatus for traffic channel set-up in atime division multiplexed (TDM) communications system having TDM slotsapproximately equivalent to a time interval of a pseudo-noise (PN) codeepoch, the apparatus comprising: means for dividing a control channelinto a first control subchannel of less than or equal to about a halfepoch in duration and a second control subchannel of less than or equalto about a half epoch in duration, the first and second controlsubchannels occurring serially in time; and means for independentlytransmitting slot allocation data in the first and second controlsubchannels to allocate respective TDM slots.
 16. A method for trafficchannel set-up in a time division multiplexed (TDM) communicationssystem having TDM slots approximately equivalent to a time interval of apseudo-noise (PN) code epoch, the method comprising: dividing a controlchannel into a first control subchannel of less than or equal to about ahalf epoch in duration and a second control subchannel of less than orequal to about a half epoch in duration, the first and second controlsubchannels occurring serially in time; and independently receiving slotallocation data in the first and second control subchannels to allocaterespective TDM slots.
 17. A method according to claim 16 wherein thecontrol channel is a paging channel.
 18. A method according to claim 16wherein receiving slot allocation data includes receiving forward slotallocation data in the first control subchannel and reverse slotallocation data in the second control subchannel.
 19. A method accordingto claim 18 further including processing the forward and reverse slotallocation data within about the next epoch, respectively, afterreception.
 20. A method according to claim 18 further includingreceiving a reverse traffic channel defined by the reverse slotallocation data staggered from receiving a forward traffic channeldefined by the forward slot allocation data.
 21. The method according toclaim 20 wherein the forward and reverse traffic is staggered at leastabout one-half epoch.
 22. The method according to claim 20 wherein thestep of receiving includes receiving the reverse slot allocation datacorresponding to reverse channel requests sent during receiving thefirst control subchannel.
 23. An apparatus for traffic channel set-up ina time division multiplexed (TDM) communications system having TDM slotsapproximately equivalent to a time interval of a pseudo-noise (PN) codeepoch, the apparatus, comprising: a processor to divide a controlchannel into a first control subchannel of less than or equal to about ahalf epoch in duration and a second control subchannel of less than orequal to about a half epoch in duration, the first and secondsubchannels occurring serially in time; and a receiver to receiveindependently slot allocation data in the first and second subchannelsto allocate respective TDM slots.
 24. The apparatus according to claim23 wherein the control channel is a paging channel.
 25. The apparatusaccording to claim 23 wherein the receiver receives forward slotallocation data in the first control subchannel and reverse slotallocation data in the second control subchannel.
 26. The apparatusaccording to claim 25 wherein the processor processes the forward andreverse slot allocation data within about the next epoch, respectively,after reception.
 27. The apparatus according to claim 25 wherein thereceiver receives a reverse traffic channel defined by the reverse slotallocation data staggered from a forward traffic channel defined by theforward slot allocation data.
 28. The apparatus according to claim 27wherein the staggering is at least about one-half epoch.
 29. Theapparatus according to claim 25 wherein the receiver receives thereverse channel allocation data corresponding to reverse channelrequests sent during receiving the first control subchannel.
 30. Anapparatus for traffic channel set-up in a time division multiplexed(TDM) communications system having TDM slots approximately equivalent toa time interval of a pseudo-noise (PN) code epoch, the apparatuscomprising: means for dividing a control channel into a first controlsubchannel of less than or equal to about a half epoch in duration and asecond control subchannel of less than or equal to about a half epoch induration, the first and second control subchannels occurring serially intime; and means for independently receiving slot allocation data in thefirst and second control subchannels to allocate respective TDM slots.